Pioneer SX-1000TA Service Manual

[Dzrout]

Does anybody have a service manual for this SX-1000TA?

Having an issue. It “works” tuner, phono, aux, tape. But volume is low. Looking to check Bias current.

 

[Dzrout]

 

[wiseoldtech]

As a professional tech, I fail to see what bias current has to do with audio level.
I see you have some test equipment there, how experienced are you in servicing audio?

 

[rayma]

Schematic, check for bad low voltage electrolytic coupling capacitors.
There are about seven of them in each channel. Just replace them.

 

[Dzrout]

As a professional tech, I fail to see what bias current has to do with audio level.
I see you have some test equipment there, how experienced are you in servicing audio?

I wanted to see if the amplifier circuit is actually fully powered up.

 

[Dzrout]

Schematic, check for bad low voltage electrolytic coupling capacitors.
There are about seven of them in each channel. Just replace them.

I am going to change all of the electrolytic capacitors either way. Just wanted to troubleshoot it a bit. I’ve replaced all the caps before on systems and found it to not always just fix the issues.

 

[wiseoldtech]

I wanted to see if the amplifier circuit is actually fully powered up.

That doesn't make any sense to me.

 

[NareshBrd]

How will a circuit be partially powered up?
Do you mean a wrong voltage?
Then that stack of equipment is there, and you have the manual.

Also, low volume is the fault with all or just one input?

 

[jacques antoine]

The hammer, to the right on the bench, looks menacing: last resort tool?
😀

 

[Dzrout]

How will a circuit be partially powered up?
Do you mean a wrong voltage?
Then that stack of equipment is there, and you have the manual.

Also, low volume is the fault with all or just one input?

On the tube amps I normally work on at, when I have a volume issue, the first think I do is check bias current. I’d there is a loading capacity or bad resistor, this will be made clear.

It’s on all input sources

 

[wiseoldtech]

Tube and transistor equipment are two widely different things, and troubleshooting each are done differently.

 

[Dzrout]

Where would you start besides the shotgun approach of replacing capacitors?

Already cleaned pots and switches.

 

[rayma]

Those seven low DC voltage series coupling capacitors per channel are rather likely to be the problem.
Parts like those will degrade sooner than others. Just one bad cap will cause a problem.

 

[wiseoldtech]

Pull out the trusty old Signal Tracer, Signal generator, and/or O'scope, and work from the output back to the input.

 

[rayma]

Old technique was signal injection, but use a series capacitor on your generator source
so the circuit DC voltages are not disrupted.

An oscilloscope is much easier though, if you have one. Just compare signals in both channels at each point.

 

[Dzrout]

Just inject a 1khz Sine wave? And follow the signal path with the scope? Compare amplitude at input to output? Easy enough

 

[rayma]

Yes, just use AC coupling on the scope, with around 0.1 - 0.5V amplitude into the stereo line inputs.
Don't run it into clipping. Keep the volume set to minimum until you get to the control itself.

Using a triangle waveform makes distortion and clipping easier to see.
Make a point of comparing the input and output nodes of each of the seven coupling capacitors per channel.

 

[Dzrout]

Thank you. I’ll recap the power supplies then do this!

 

[Dzrout]

Update:

Started in the power supply, replaced all the capacitors in every board, after I finished the Tone control board, the receiver started working fantastic. Thank you for your help!

 

[rayma]

Good work.